Apply the distributive property to factor out the greatest common factor. $9+12n =$
Solution: $ 3$ is the greatest common factor of $9$ and $12n$. $\phantom{=}9+12n$ $={3}\cdot 3+{3}\cdot 4n$ $={3}(3+4n)~~~~~~~~$ Apply the distributive property. The answer: $ {3}(3+4n) $